The disclosure of Japanese Patent Application No. 2002-221638 filed on Jul. 30, 2002, including its specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an exhaust gas purification device and method of an internal combustion engine and, more particularly, to an exhaust gas purification device of an internal combustion engine capable of curbing degradation of emissions even when the output of the engine increases during a catalyst warm-up.
2. Description of the Related Art
In internal combustion engines that use gasoline or the like as a fuel, a catalyst (e.g., a three-way catalyst, a nitrogen oxides storage-reduction catalyst, a catalyst having an oxidizing function, etc.) is disposed in an engine exhaust system so as to remove nitrogen oxides, hydrocarbons and carbon monoxide from exhaust gas.
In order to reduce nitrogen oxides and oxidize hydrocarbons and carbon monoxide on such a catalyst, it is necessary to keep the amount of oxygen stored in the catalyst at about half the limit amount of oxygen storage and control the air-fuel ratio of exhaust gas discharged from the internal combustion engine within a window around or near a stoichiometric air-fuel ratio.
Therefore, in order to control the exhaust gas air-fuel ratio at the stoichiometric air-fuel ratio, an air-fuel ratio sensor (an O2 sensor or an A/F sensor) for detecting the air-fuel ratio of exhaust gas that is disposed at an inlet to the catalyst. Then, an air-fuel ratio feedback control for controlling the amount of fuel supplied to the engine on the basis of the output from the sensor is performed.
However, the catalyst is unable to normally perform its function unless the air-fuel ratio has been activated and the catalyst warm-up has been completed. Therefore, until the activation of the sensor and the warm-up of the catalyst are completed after a startup of the engine, the air-fuel ratio feedback control is prohibited and the warm-up of the catalyst is accelerated by dedicated measures.
In a conventionally employed procedure for accelerating the warm-up of a catalyst, injection of a secondary air into the exhaust pipe of the engine (hereinafter, referred to as xe2x80x9cAIxe2x80x9d) is performed to increase the oxygen concentration in the exhaust gas and therefore accelerate oxidative reactions on the catalyst. The reaction heat thus produced accelerates the warm-up of the catalyst.
However, the catalyst warm-up cannot be immediately achieved, because a certain amount of time is needed before completion of the warm-up.
Therefore, in a situation immediately following a start of the AI operation where the catalyst warm-up has not sufficiently progressed and there is no effective performance of exhaust gas purification, it is required that the AI be continued in order to accelerate the catalyst warm-up even if the amount of exhaust gas increases due to an increased output of the engine when the vehicle is initially driven or the like.
However, in a situation where a considerable amount of time has elapsed following a start of the AI and the catalyst has partially acquired an exhaust gas purification capability, it is desirable that the AI be stopped to actively improve the quality of emissions if the amount of exhaust gas increases due to an increased engine output.
It is an object of the invention to provide an exhaust gas purification device of an engine capable of curbing degradation of emissions during a catalyst warm-up based on the AI operation by stopping the AI in accordance with the degree of catalyst warm-up if the output of the engine increases during the catalyst warm-up.
An exhaust gas purification device of an engine in accordance with a first aspect of the invention includes: a catalyst disposed in an exhaust gas pipe of the engine for purification of an exhaust gas; a secondary air injection device for injecting a secondary air into the exhaust gas pipe upstream of the catalyst so as to accelerate a warm-up of the catalyst at a time of a startup of the engine; a controller that: detects a degree of the warm-up of the catalyst with a warm up detection device; calculates a criterion output based on the degree of the warm-up detected by the warm-up detection device; detects an output of the engine with the output detection device; and stops injection of the secondary air with an injection stop device provided that: the degree of the warm-up detected by the warm-up detection device is greater than or equal to a predetermined criterion degree of the warm-up; and that the output of the engine detected by the output detection device is greater than or equal to the criterion output calculated by the controller.
According to the above-described construction, if the output of the engine becomes greater than or equal to a predetermined output during the secondary air injection (AI) operation, the AI is stopped provided that the warm-up of the catalyst has progressed to a certain degree.
In the above-described construction, the warm-up detection device may detect an accumulated value of an amount of flow of a primary air taken into the engine after the startup of the engine. Therefore, the degree of warm-up of the catalyst can be determined on the basis of the accumulated value of amount of intake air following the engine startup.
In the foregoing construction, the output detection device may detect the output of the engine based on a degree of opening of a throttle valve. Therefore, the engine output can be detected on the basis of the degree of opening of the throttle valve.
In the foregoing construction, the output detection device may detect the output of the engine based on an amount of intake air taken into the engine. Therefore, the output of the engine can be detected on the basis of the amount of intake air.
The exhaust gas purification device may further include a cooling water temperature detection device for detecting a temperature of a cooling water of the engine, wherein the controller corrects the criterion output and the criterion degree of the warm-up based on the temperature of the cooling water detected by the cooling water temperature detection device. Therefore, the criterion output and the criterion degree of the warm-up can be corrected on the basis of the cooling water temperature.
It is another object of the invention to provide a method for purifying an exhaust gas for an engine. This method includes: purifying the exhaust gas with a catalyst disposed in an exhaust gas pipe of the engine; injecting a secondary air into the exhaust gas pipe so as to accelerate a warm-up of the catalyst. A criterion output is calculated based on the degree of the warm-up detected, and an output of the engine is further detected. Injection of the secondary air is stopped such that the degree of the warm-up detected is greater than or equal to a predetermined criterion degree of the warm-up, and such that the output of the engine detected is greater than or equal to the criterion output calculated.